JPS61148414A - Compact zoom lens - Google Patents

Abstract

PURPOSE:To make a zoom lens compact by providing the 1st lens group with positive refracting power and the 2nd lens group with negative refracting power, forming the 1st lens group and the 2nd lens group in zooming constitution, and using a distributed index lens as at least one of lens elements. CONSTITUTION:The 1st lens group 11 is provided with the positive refracting power and the 2nd lens group 12 is provided with the negative refracting power. The 1st lens group 11 and the 2nd lens group 12 are formed in the two-group type zooming constitution in which both groups are moved to the object side for zooming from the wide-angle end to the telephoto end while their on-axes gap is decreased. Further, radial type distributed index lenses are used as the 1st lens (R1 and R2) of the 1st lens group 11. Those distributed index lens elements (R1 and R2) are used to shorten the overall optical length of the whole system. Thus, the distributed index lens elements are employed, so the number of lens elements is decreased to make the constitution compact and aberrations of the respective lens groups are compensated and reduced, thereby reducing aberrational variation.

Description

[Detailed description of the invention] (Technical field) The present invention relates to improvements in zoom lenses.

(Prior Art) In recent years, with the miniaturization of cameras, there has been a growing demand for compact zoom lenses with short overall lengths. Even in the field of small cameras that do not have interchangeable lenses, such as lens-shutter cameras, there is a growing demand for zoom lenses to be installed, rather than larger and inconvenient cameras such as single-lens reflex cameras with interchangeable lenses. There is a growing demand for something that is large enough to fit in a box and is easy to carry.

In order to meet these demands, the present applicant has
201213, etc., the lens is composed of a homogeneous glass lens, the first lens group has a positive refractive power, the second lens group has a negative refractive power, and the distance between the first lens group and the second lens group is changed. We have proposed lenses that have variable magnification.

However, in the case of the above-mentioned configuration, one way to make the lens compact is to tighten the power arrangement of each lens group, but this increases aberration fluctuations during zooming. In order to reduce the amount of aberration fluctuation, it is effective to increase the number of lenses to suppress the occurrence of aberrations, but this would inevitably increase the size of the entire lens. Furthermore, when reducing the power to suppress fluctuations in aberrations, the amount of movement of the lens group must also be increased, which is contrary to the requirements, making it difficult to make the lens compact.

(Objective) An object of the present invention is to provide a zoom lens that is capable of suppressing fluctuations in aberrations to an extremely low level, is compact, and has a small number of lenses.

In order to achieve the above object, at least one lens group of a lens system in which zooming is performed by decreasing the axial distance between the lens group and the second lens group from the wide-angle end to the telephoto end. at least one that shares the optical axis
A gradient index lens is provided.

Incidentally, gradient index lenses are already well known in literature, etc.
This is a lens in which the refractive index is distributed non-uniformly within the lens according to a predetermined law. More specifically, it includes a radial type in which the refractive index changes in a direction perpendicular to the optical axis of the lens, that is, in the radial direction, and an axial type in which the refractive index changes in the direction of the optical axis of the lens.

In the case of the radial type, the inside of the lens also has refractive power, and when this lens is used, it is possible to transfer light not only through surface refraction but also when the light passes through the lens.

Since there is curvature, when considering a lens with the same refractive power as a homogeneous glass lens, the radius of curvature of the lens becomes looser, which is effective in correcting spherical aberrations and the like. In addition, the Petzval sum P inside the lens is the power due to internal convergence and divergence, when the focal length of the entire system is IK normalized, the refractive power ψ of the lens, and the axial refractive index No, P = ψ/N This is smaller than the occurrence P=ψ/N on the surface of a normal lens, and the field curvature can be reduced. Aku -.

In the case of the serial type as well, the refractive index varies depending on the incident position of the light ray, and it is effective for correcting spherical aberration and higher-order aberrations.

In particular, this type of compact zoom lens tends to have an undersized image plane, so using a lens with a radial refractive index distribution as a positive lens can correct the field curvature with a small Petzval sum. As mentioned above, since the white base becomes loose, the occurrence of spherical aberration can be reduced.

[Description of Embodiment] FIG. 1 shows a first embodiment of the present invention. 11 is a first lens group with positive refractive power, 12 is a second lens group with negative refractive power, and the first lens group 1 is used for zooming from the wide-angle end to the telephoto end.
The first and second lens groups 12 constitute a two-group zoom lens with a short pack that moves toward the object side while decreasing the axial distance.

In this embodiment, the first lens (R1e
R2) A K radial type gradient index lens is used. Normally, with this type of zoom lens, if the first lens group has the same power, four or more lenses are required to obtain the same image quality, but this For example, by introducing one gradient index lens whose refractive index tends to decrease from the optical axis to the outer periphery, the total length of the first positive lens group is shortened by the simple configuration, We have succeeded in shortening the total optical length of the system.

Furthermore, as mentioned above, this gradient index lens keeps the Petzval sum small and the curvature of field small. By controlling the high-order distribution coefficients of the gradient index lens, fluctuations in spherical aberration and comatic aberration are also kept to a minimum, thereby suppressing fluctuations in aberrations that tend to occur in compact zooms of this type with tight refractive power arrangements.

FIG. 3 shows a second embodiment, in which 21 is a first lens group with positive refractive power, 22 is a second lens group with negative refractive power,
It constitutes a telephoto type two-group lens. This embodiment employs two high-dispersion refractive lenses in the first lens group 21, with the first lens (R1, R2) being a radial type lens, and the third lens (Rs, Rs) being an axial type lens. This allows for a 2x zoom ratio while maintaining performance.

Although this example was able to increase the variable power ratio while keeping the overall length short, the gradient index lens of the first lens in the first lens group 11 has the same effect as described in Example 1. However, the purpose of the third lens is to help correct aberrations, which has become difficult due to the increased zoom ratio.

A third embodiment is shown in FIG. 31 is a first lens group with positive refractive power, and 32 is a lens group with negative refractive power, which constitutes a telephoto type zoom lens with a short back.

In this embodiment, the first lens (Ry-R
s) K This is an example in which a lens having a refractive index distribution in the radial direction is introduced. The second lens group 32 has a larger movement amount than the first lens group 31, and if the aberrations here are corrected to a small value, a lens with small aberration fluctuations can be obtained. This embodiment is particularly effective in reducing fluctuations in spherical aberration.

The fourth embodiment is an advanced version of the two-group zoom lens, in which a third lens group is disposed adjacent to the second lens group, and a gradient index lens is used for the third lens group.

In the fourth embodiment (FIG. 7), the lenses of the third lens group 43 include lenses with a refractive index distribution in the radial direction, but the third lens group 43 is a fixed group during zooming. By introducing a gradient index lens here, it has become possible to correct fluctuations in image plane tilt due to zooming. Although the third lens group 43 has a negative refractive power in this embodiment, it may have a positive refractive power depending on the method of sharing the refractive power with the second lens group. However, in any case, it has only a very weak refractive power compared to the refractive power of the entire system.

Further, in this embodiment, the third lens group 43 is fixed, but the second lens group 43 is fixed.
It may be moved in the optical axis direction simultaneously with and independently of the lens group 42.

Lens data of Examples of the present invention will be described below.

In addition, R1 is the first one-height radius in order from the object side, Di is the thickness of the first surface and the air gap, and Ni and νi are the refractive index and Abbe number of the first lens. N (h).

Those denoted by N(x) etc. indicate gradient index lenses.

Isao 12I2 幡#agony country engineering agony agony Lerorocri inside 2! :Z Mouth 0 Mouth 0 (Effects) According to the present invention explained above, the number of lenses in each lens group of a zoom lens can be reduced, making it lighter and more compact. Since the number of lenses in the lens group can be reduced and the length of the lens groups can be made smaller, there is more space between each lens group, and the range of movement of the moving group can be increased, making it easier to achieve high variable magnification. . Furthermore, since the number of lenses constituting each lens group of the zoom lens can be reduced, the distance between each lens can be reduced, and the overall length can be significantly shortened.

On the other hand, since aberrations can be corrected to a smaller value in each lens group, it is possible to achieve a zoom lens with small aberration fluctuations due to zooming. In addition, since the generation of Petzval sum is small, the power of each lens group can be strengthened, and the total length can be shortened. This has the effect of reducing the occurrence of next-order aberrations.

[Brief explanation of the drawing]

FIG. 1, FIG. f43, FIG. 5, and FIG. 7 are lens cross-sectional views and FIG. FIG. 4, FIG. 6, and FIG. 8 are aberration curve diagrams, respectively. In the figure, 11.21.31.41 is the first lens group, 12.
22, 32, and 42 are the second lens group, and 43 is the third lens group. Figure 6: Pick up! ! Non-employee basis Distortion 'Procedural amendment (voluntary) December 11, 1985 Michibe Uga, Commissioner of the Patent Office 2, Name of the invention Compact zoom lens 3, Relationship with the person making the amendment Patent applicant's residence Address: 3-30-25 Shimomaruko, Ota-ku, Tokyo 148, Specification subject to amendment 9 Drawing 6, Contents of amendment (1) "r125" on page 14, line 16 of specification path has been corrected to r150J, and r150J That one is r200
Correct it with J. (2) Correct Figure 8 as shown in the attached sheet.

Claims (4)

[Claims] (1) Consisting of two or more lens groups, starting from the object side,
The first lens group has positive refractive power, the second lens group has negative refractive power, and the lens performs zooming by decreasing the axial distance between the first lens group and the second lens group from the wide-angle end to the telephoto end. A compact zoom lens characterized in that at least one lens group includes at least one gradient index lens that shares an optical axis with another lens. (2) A compact zoom lens according to claim 1, wherein the refractive index of the gradient index lens changes in the radial direction. (3) A compact zoom lens according to claim 1, wherein the refractive index of the gradient index lens changes in the optical axis direction. (4) A patent in which the gradient index lens has two lenses, one of which has a refractive index that changes in the radial direction, and the other one that is a gradient index lens that has a refractive index that changes in the optical axis direction. A compact zoom lens according to claim 1.